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When the supercharger is spinning at part throttle, there is an internal vacuum controlled bypass valve that opens allowing the air to recirculate through the supercharger so that it is not compressed. This reduces frictional losses at part throttle, when the throttle is opened, the manifold vacuum falls and the valve closes allowing the supercharger to build boost. Some supercharger kits have a blow off valve that does the same thing but we like this clean internal self contained method better.
You can see the Sprintex's screw shaped rotors that diverge at the end of the housing compressing the air internally. This is different from the lobe shaped rotor of a typical roots blower that simply moves the air past the blower allowing it to back up and compress inside the plenum of the intake manifold. The external compression of the roots blower is far less efficient. You typically see numbers of about 50% which means more crank power robbed and more heating of the intake charge air, as high as 300 degrees or even more under some conditions! Compare this to our blower's 70% efficiency.
Here is a cutaway drawing of the actual blower used on the FR-S. You can see the diverging screws and can visualize how they can provide efficient internal compression versus the lobes of the traditional roots positive displacement blower that simply moves a higher volume of air allowing it to squish in the intake plenum assuming that the blower moves more air volumetrically than the motor.
Here is the compressor map for our Sprintex S5-210 blower. Note how wide the 70% island is. Our blower will be operating at peak efficiency for most of the engine's operating range! A centrifugal compressor like that used in some other supercharger kits might reach a higher peak efficiency but it will have a more narrow operating range. A positive displacement screw blower might have just a few points less peak efficiency but will have a lot of area under the sweet spot curve.
More power means more combustion pressure and more heat. Since our car is going to be track driven, we have to deal with the heat. We got a large capacity drop in radiator from Koyo Cooling Systems to help keep things happy. The Koyo radiator has an all aluminum core with about 40% more capacity and TIG welded aluminum end tanks.
The Koyo is deigned to drop in perfectly with provisions for the factory fans and brackets. Innovate Motorsports' R&D test mule FR-S has run this radiator in 100 plus degree Arizona heat on the track with water temperatures remaining totally in control.
We found the radiator to live up to its claims of perfect fit and easy drop in installation.
